RED UFO

My AC clutch does not engage.

I tested the AC clutch fuse (#2) with my meter and I have 12.30V there. When I test the Blue and Black wires at the AC clutch plug there is no reading. When I test each wire for ground I have ground on both even if I have the connector unplugged.

Does anyone have any ideas?

Is the blue wire 12V and Black Ground?

The previous owner had the air fixed last summer for $200. I bought it in December and come spring it didn't work.

aminnich

Check power at the binary switch. Or just take a paperclip and jumper the switch. I would bet you have low freon charge and the binary switch is protecting the compressor by not letting the clutch engage. which is what it is supposed to do.

RED UFO

I see two sensors, one on the upper low pressure line and one on the bottom high pressure line. Do I jump them both? My FSM shows them linked in series.

schrade

Witout seein' 'em, I can't tell ya' which one it is. BUT, of the 2, one of 'em has 1 wire with continuity to the A/C compressor connector - probably the same color wire too.

That's the switch to test jump. DON'T hold it jumped too long if it engages the clutch. Like aimich said, it's off for a reason - low freon.

gw962

If you have the C68 electronic controller, push both fan speed buttons until -00 appears on the readout. Push 'Auto' and it should show a code. If it shows 09, it's reading low freon charge.
I had this on mine Thursday but it turned out that the Low pressure switch was bad. $11 and 10 minutes and I had cold air.
You can do a short test by using a paperclip to jumper the connector on the switch. If the compressor kicks on with cold air, replace the switch. If no cold air, you'll have to recharge the system.

RED UFO

I did have a code 09. I will follow these procedures and I will report back.

Thank you

RED UFO

I tried jumping both sensors and I got nothing. It doesn't appear I am getting 12V from the relay to the sensors. I also put a gage on the Low side and I am reading between 46-65 PSI which is too high for a R-134 conversion.

Even with the high PSI reading I think there is a problem with the relay or the controller.

I read in the FSM that the presence of the 09 code will disable the signal from the controller to the relay. I will clear the code in the morning and see what happens.

I am still concerned about the High PSI condition. What would cause that? Could it be because the compressor is not running?

theadmiral94

not sure about your year, but here's info for a 94 with R134a freon:

The sensor on the high pressure line (thinner line heading to the cabin) is a pressure sensor (effectively a variable resister) -- the ECM feeds it 5 vDC and measures the returned voltage. it is used to turn off the compressor if too high a pressure, and to set the '09' code on the AC electronic control head if pressure is too low.

The sensor on the low pressure line (top fatter line from cabin) is a compressor clutch cycling switch, openning and closing the 12 vDC to the compressor clutch based on pressure (compressor cycles on at 41-51 psi ;; compressor cycles off at 20-28 psi). Given summer temps, compressor will likely run all the time, assuming inside fan is on.

If the pressure you mentioned is Low side, WITHOUT the compressor running, it may not be too high (e.g. for R134a, at 75* F, would be 78 PSI.

Regarding the relay location: on the 94, they appear to be mounted to the rear side of the passenger side wheel well.

RED UFO

Thanks

I do have a 09 code but the low side is reading between 45-65 PSI without the clutch running. My FSM shows the running in series between the relay and the clutch. I would think that if one sensor is open the clutch won't engage.

I can also see why the PSI needs to be in the 41-51 range. That is what the AC clutch sensor is looking for to send 12V to the clutch. The R-134 charging kit calls for 25-45 to be normal. I think that would be the case if the car was build with R-134 in it.

As I mentioned, I read in the FSM that if the 09 code is present that the control unit won't trigger the relay to send 12VDC to the clutch.

It is raining out so I will try resetting the code in the morning.

I hope I am on the right track

RED UFO

Success

I have cold air @ 49-52 degrees.

It turns out it was low freon all the time. I feel a little stupid after what I went through to get to this point. Maybe ignorant is a better term.

I guess you learn by trial and error so I hope this final post in this thread helps someone else.

I have never worked on A/C before. I had help from members on the forum and a FSM.

It all started when I had no power to the clutch. I bought a R-134 recharge kit with a trigger and a gage. When I hooked up the gage it read 50 PSI ("Danger Will Robinson Danger"). I couldn't even get 12V to the low pressure sensor/switch. I had a code 09 on the C68 electronic control head LCD.

This is what I was doing wrong.

When the freon is low the low pressure sensor/switch on the large (low-side) freon tube sends an 09 code to the CCM and it displays on the programmer. Once this 09 code is registered the trigger wire to the AC clutch relay shuts off so the compressor won't run. You have to disconnect the negative battery cable for a minimum of 1 minute. This clears the code and will allow the clutch to engage. What I didn't know is that when I tested the PSI on the low side the compressor wasn't running so the PSI was in the danger zone. Once I figured this out I cleared the 09 code and jumped the low pressure switch to keep the compressor running. Now I saw low pressure on my gage so I just started injecting my R-134. The pressure rose to about 27 PSI and it started blowing cold, very cold. I hooked up the low pressure switch and everything is dandy.

I hope my learning experience helps someone else.

P.S. To see if you have the 09 (low Freon) code, hold the up and down fan buttons in for five seconds. 00 will appear on the LCD. Push the middle fan button and the 09 code will appear if your freon is low or you have a bad pressure switch.

Thanks to all,

Al

aminnich

Good to hear you got it fixed.

WAR EGIL

Help!!!! I have a 94 with the same problem as RED UFO - A/C clutch does not engage.
But, I do not get an 09 code (bummer). So, what to check next?

SunCr

It was pretty much outlined for you. The PCM - actually the Programmer - on these years monitors the Low Pressure Switch for how often it's opening and closing. Should it open and close too rapidily, it's programmed to recognize that as a low charge and ground is removed from the Compressor Relay. A trouble code is also set in the Processor and until that code is cleared from memory, a signal isn't going to reach the PCM to drive the Compressor Relay. You clear the code by removing power or simply disconnecting and reconnecting the battery. And if you don't fix the low charge condition, the code will reset and the whole process begins anew.

The PCM monitors the Pressure Sensor on the high pressure line. Whatever that signal is (1 volt equals 100 psi), it looks for it to rise the minute the compressor engages. If it doesn't, it removes ground from the compressor relay and sets a code for the Sensor (something in the 70's - if I remember right - for an OBD1; in the 570's for an OBD2). It also monitors that sensor's input to turn on the fans and if the Pressure (voltage) gets high enough to indicate that something might blowup, it will remove ground from the Relay.

In short, the 09 means your Vette is out of gas - or the processor thinks that it is. You need to find out where your gas went, fix the leak and recharge and if you want the a/c to run afterwards, clear the code.

WAR EGIL

I do not get an 09 code to erase. Also, there are no DTC error codes.
I did disconnect the battery, just in case.

RED UFO

See if you have 12V coming out of the relay to the Low Pressure switch. Do a pressure test on the freon. you should have about 25-30 PSI. If you do and you have power coming out of the relay then bypass the pressure switch and see if you are blowing cold. Just don't run it to long this way unless you are sure you have freon. If it blows cold when you have the switch bypassed you have a bad switch.

RED UFO

My car is a 91 so yours may be different. I could not have figured mine out without the FSM.

SunCr

Sorry - missed the fact that you don't have a Code. I'd guess that it has an intermittent open at the low pressure switch. It seems fairly common for this Year to have a problem there. Jumper the harness connector with a paper clip. If that gets it running, it usually needs a new connector and/or switch. To see if the switch is bad, check for continuity across it's contacts. It takes 50 psi for any Year - not 25 or 30 psi - to close them and even a 1/2 lb of gas will make that when it's sitting still (ie, a/c off). If they are closed and it's not running, it's in the connection; but not always the connector. When I had this problem with my truck, it took a new switch to correct it. Others have posted similar; predominately on the '94 - why I don't know. If this isn't it, the Relay is dead or the PCM isn't getting the clutch request. You'll need a scanner to check that out.

RED UFO

SunCr,

Please clarify something for me. My FSM does say the switch closes between 41-51 PSI. When I charged today it took 3 1/2 cans and the highest reading I got on the gage was 27.

Why is that?

SunCr

Wow - that's a lot of gas - the R12 fill is 2.25 lbs or 36 ozs or 3 cans - though sometimes you don't get everything out of a can. Anyway, 1 can would have given it 50 psi (assuming it above 50 degrees) and either your gage is broken, or it's leaking out as it sucks it in. If you can't see a leak, did you get any ice on the windshield or frost on the vents. A leaking evaporator will often show up at one or the other - partcularly since R12 (and R134) is below 0 at normal atmospheres. Check the low pressure switch contacts for a closed circuit and if they're open, drive by an a/c shop for a leak test - often it's on the cheap because they want the big $'s to fix it (or just go to Poop Boys - todays ad in the Sunday Funnies had their a/c "Performance Tuneup" at $29). A competent tech can go over everything in about 5 minutes. He/she will use an electronic leak detector and given that it's a GM, probably stick it in the vents first (and of course replacing the Evaporator is one of the more expensive - profitable - repairs).

SunCr

It occurred to me that maybe we're not on the same page, so here's the deal on charging and checking operating pressures:

If it's been exposed to the atmosphere, you've got to get the air out and for that you need a vacuum pump. You connect the center (charge) or yellow hose of your gages to the pump and then the low (blue) to the low side and the high (red) to the high. Turn on the pump and open both the low and high side valves. Run the pump until you achieve 28 inches of mercury on your Low Side Gage (assuming you're somewhere close to sea level) and if you want to beat whatever the Factory did, run it for an hour. Close both valves and turn off the pump and wait 20 minutes to make sure that the vacuum holds. If it does, disconnect the pump and connect a can to the Yellow or low side hose and momentarily crack that hose to purge any air. Then open the Low Side Valve ONLY. Let the vacuum suck in that first can. When empty, close the valve. Your low side gage should now indicate the static or non operating pressure and if it's 70 degrees or better, that pressure should be enough to close the Low Pressure Switch contacts; ie, above 50 psi. You finish charging by starting the engine and blocking the throttle so that it's running at 1200 rpms. Because you only have 12 ozs in it, the liquid that reaches the Evaporator is going to immediately flash into a gas and by the time it reaches the low pressure switch, all the oomph will be gone and the compressor is going to cycle off. That makes charging difficult, so to keep it running, and before you turn on the a/c, jumper the low pressure switch contacts with a paperclip. Then, turn the a/c on max, connect your second can - again cracking the yellow hose momentarily to purge air - and open the Low Side Valve ONLY to let the system pull in the charge. When that second can is empty, close the valve and let the system run for a minute or two and then check your pressures. A high side pressure of 2.2 to 2.5 times the temperature of the air across the condensor is a good measure of a realistic charge and when you get that, the low usually falls into an acceptable range. And as to the low side, R12, at 30 psi, is 32 degrees. R134, at 28 psi, is the same. So, you want the Low side to be a few psi below or above these pressures and you should be able to achieve that as long as the air across the Condensor isn't above 90 to 95 degrees. And if it's below these numbers, connect a third can and continue as previously outlined, only this time, stop when that can is about half empty; ie, close the valve, let the system stabilize and recheck your High and Low Side pressures before adding any more gas. At this point, it will also help to check your center vent temp so stick a digital thermometer in there and see what it is.

A couple of other things: the cooling fan(s) need to be running and not cycling on and off. That's easy for the '85 to '89 as disconnecting the fan switch (on the high pressure line) will keep the fan on. The '90 and above drive the fan(s) based on inputs from the pressure sensor and there is virtually no way to change that input. Therefore, for these years, wait until they are both cranking before taking a moment to observe pressures. That usually takes at least a couple of cans or 2/3's of the full charge.

When you're satisfied with your operating pressures, remove the jumper from the Low Pressure Switch connector and plug it back in. Then with the system on max, disconnect the Blower Motor. That will drop the low side and the system will cycle off. Note that pressure. For R12, you want it cutting out at 25 psi; for R134, 22.5 psi. Most Low Pressure Switches are adjustable and between the contacts there is a screw. Turn it counterclockwise to reduce the cutoff threshold, clockwise to raise it. Adjustments should be made 1/2 turn at a time.

Hope this helps. The point is that pressures are only going to be accurate with the Valves on your Gage Set closed and your compressor needs to be running at something close to max efficiency (hence 1200 rpms), and the cooling fan(s) has to be blowing air across the condensor. If you want to post your operating pressures - obtain them as above and note the outside air temp or better yet, the temperature of the air at the Condensor (generally 10 degrees higher on a bottom feeder like the Vette). I find that the Outside Air Readout for the Electronic units works well for this data as the sensor is mounted close by.